A number of techniques have been developed to treat occlusive diseases of the heart, such as atherosclerosis. For example, stenosis of the coronary arteries typically is treated using bypass grafting techniques. More recently, minimally-invasive techniques, such as percutaneous transluminal angioplasty and atherectomy, have been developed that use catheter-based systems to disrupt or remove a stenosis. Techniques such as transmyocardial revascularization ("TMR") also have been developed, in which a high-energy laser is used to ablate a matrix of channels in the myocardial tissue to enhance perfusion.
More recently, attempts at stimulating revascularization of cardiac tissue have focused on the use of the angiogenic factors. For example, Schumacher et al., "Induction of Neoangiogenesis in Ischemic Myocardium by Human Growth Factors," Circulation 97:645-650 (1998), report that intraoperative injection of fibroblast growth factor (FGF-I) into the myocardium of 20 patients suffering from stenosis of the internal mammary artery/left anterior descending coronary artery resulted in the development of new capillary vessels radiating outward from the injection point in 4 days.
By comparison, however, Fleischer et al., "One-Month Histologic Response of Transmyocardial Laser Channels With Molecular Intervention," Ann. Thorac. Surg., 62:1051-8 (199), report that a single dose of vascular endothelial growth factor (VEG-F), administered intraoperatively at the time of laser TMR, showed no significant increase in myocardial vascularity. It was hypothesized that longer residence of the VEG-F may be required to stimulate angiogenesis.
In view of the foregoing, it would be desirable to provide methods and apparatus for percutaneously injecting therapeutic agents, such as drugs or angiogenic growth factors, into myocardial tissue to promote revascularization.
It also would be desirable to provide methods and apparatus for percutaneously injecting diagnostic agents, such as radio-isotopes or contrast agents, into myocardial tissue to enhance diagnosis of cardiac ischemia.
Apparatus and methods are known for injecting pharmacological agents into the walls of vessels, and surrounding tissue, to reduce restenosis following the use of minimally-invasive techniques, such as angioplasty. For example, angioplasty balloons often injure a large percentage of the endothelium that they contact, and the healing response may itself lead to recurrence of the stenosis. Methods and apparatus therefore have been developed for injecting drugs, such as anti-platelet, anti-coagulant, anti-proliferative and/or anti-inflammatory drugs, into the wall of a treated vessel, or adjacent tissue, to discourage restenosis.
For example, U.S. Pat. No. 5,464,395 to Faxon et al. describes a system for delivering therapeutic or diagnostic agents to tissue surrounding a vessel. A needle cannula having a tissue-piercing tip is extended from a delivery catheter to penetrate a selected distance into tissue surrounding the vessel to inject a therapeutic or diagnostic agent. The device includes a balloon for dilating the vessel prior to extending the needle cannula. If multiple needle cannulas are used, each needle cannula requires a separate lumen and must be individually positioned within the tissue to be treated.
U.S. Pat. No. 5,693,029 to Leonhardt describes a catheter having a plurality of fixed-length needle assemblies that are selectively extended to pierce the walls of a lumen and inject a therapeutic agent. The therapeutic agent is delivered to the needle assemblies via a common channel. The catheter includes a balloon that is inflated to deploy the needle assemblies, and a retraction mechanism that retracts the needle assemblies once the balloon is deflated.
The foregoing devices have a number of disadvantages that limit the utility of those devices for delivering therapeutic or diagnostic agents in the heart. For example, each needle cannula in the Faxon device must be separately deployed and positioned; consequently, the use of multiple needle cannulas may be both time consuming and laborious. Similarly, because the Leonhardt device employs relatively short fixed-length needle assemblies, that device cannot be used for administering a therapeutic or diagnostic agent at various depths within the myocardium. In addition, the retraction mechanism used in the Leonhardt device inherently poses risks to the patient's health should that mechanism fail.
It therefore would be desirable to provide methods and apparatus for administering a therapeutic or diagnostic agent at multiple sites in extravascular tissue, but that does not require time consuming and laborious in-situ assembly.
It also would be desirable to provide methods and apparatus for administering a therapeutic or diagnostic agent at multiple sites in extravascular tissue at various depths.